The present invention is directed to a free machining aluminum alloy and, in particular, to an aluminum alloy utilizing a high melting point material as a free machining constituent thereof.
Free machining aluminum alloys are well-known in the art. These alloys typically include free machining constituents such as lead, tin, indium and bismuth for improved machinability. In many of these alloys, these constituents form low melting point compounds which readily melt or soften due to the friction heat created during machining. With the melting or softening of the low melting point compounds, material removal as part of the machining process is easily facilitated.
One of the drawbacks with these types of free machining alloys is the tendency for the free machining constituents to deform or flow with the matrix material being worked by the machining tool. Since these free machining constituents, either in elemental or compound form, have a relatively low melting point, their flow properties tend to match those of the aluminum matrix. Consequently, when the aluminum matrix deforms due to machining, the low melting point elements or compounds tend to deform in a similar fashion. The tendency for the free machining constituent to deform with the metal matrix retards formation of voids in the alloy. Void formation as a result of machining is a preferred mode for metal removal since it enhances generation of finely sized machining debris. By delaying the void formation and subsequent material removal through the generation of machining chips, the machining tool does more work and tool life is reduced.
In light of the drawbacks noted above with respect to prior art free machining aluminum alloys, a need has developed to provide an improved free machining alloy which enhances the machining process.
In response to this need, the present invention provides a free machining alloy containing a volume fraction of a high melting point free machining constituent that enhances void formation during machining.
Accordingly, it is a first object of the present invention to provide an improved free machining aluminum alloy.
Another object of the invention is to provide a free machining aluminum alloy utilizing one or more high melting point machining constituents for increased machine tool life.
A still further object of the invention is to provide a method of machining an aluminum alloy material by utilizing a free machining aluminum alloy containing an effective amount of a high melting point free machining constituent.
Other objects and advantages of the present invention will become apparent as a description thereof proceeds.
In satisfaction of the foregoing objects and advantages, the present invention is an improvement over prior art aluminum alloys containing one or more free machining constituents. According to the invention, an aluminum alloy is modified with a free machining constituent. The free machining constituent comprises at least one or more high melting point materials. The high melting point materials comprise between about 0.1% and about 3.0% by volume of the free machining aluminum alloy.
A more preferred volume percent ranges between about 0.2% and 2.0% with an even more preferred range being between about 0.3% and 1.5%. Another preferred range is between about 0.4% and 1.0%.
The high melting point material can be any material which is essentially insoluble in the aluminum alloy matrix and is one that remains stable or does not soften or melt during the machining operation. The melting point of the material should be greater than the melting point of the aluminum alloy matrix. The melting point of the aluminum is about 1220xc2x0 F. (660xc2x0 C.). Thus, materials meeting the requirements above that remain solid in spite of the matrix material melting or softening are candidates as the free machining constituent of the invention.
The high melting point material can be one material or a combination of different materials providing that the mixture remains within the volume percents recited above.
The high melting point material can be either in elemental form or in the form of a compound. Examples of; high melting point compounds include carbides, nitrides, borides, silicides, oxides, aluminides or combinations thereof. Elements include boron, carbon or graphite, various refractory elements and the like.
The invention also includes providing a workpiece made from the inventive aluminum alloy composition and subjecting it to a machining operation to form a desired shape. The machined product containing the inventive aluminum alloy composition is also within the purview of the invention.